Carbohydrates such as glucose and mannose are ionizable to anions at high pH and can therefore be separated on anion exchange chromatography columns in sodium hydroxide eluents.
Known anion-exchange compositions generally fall into several categories. In the more traditional anion-exchange systems, synthetic support resin particles, generally carrying a negative charge, are covered with a layer of smaller synthetic resin particles carrying anion-exchange functional groups of positive charge, i.e. anion-exchange sites. The smaller particles are retained on the larger support particles via electrostatic attraction. The support resin can take a variety of forms. See for example U.S. Pat. Nos. 4,101,460; 4,383,047; 4,252,644; 4,351,909; and 4,101,460.
A more recent development utilizes an uncharged support resin and smaller latex particles containing anion-exchange functional groups, held together by a dispersant. See U.S. Pat. No. 5,324,752.
In addition, methods have been developed to eliminate the smaller latex particles altogether. For example, an anion exchange functionality is grafted, or covalently bonded, to a variety of polymeric substrates; see for example U.S. Pat. No. 5,066,784. Alternatively, the anion-exchange functional groups are not covalently attached but are tightly associated with the support resin particles, either electrostatically or otherwise; see U.S. Pat. No. 4,927,539.
In carbohydrate analysis, analytes with hydroxyl groups with suitable stereochemical configurations, such as sugar alcohols and mannose, show severe chromatographic peak tailing when borate is present in the eluents. This peak tailing, or peak asymmetry, causes the peak to differ from Gaussian distribution with a peak asymmetry value of 1.0. Larger peak asymmetry numbers indicate greater peak tailing. This peak tailing can render the identification and quantification of the carbohydrate analytes difficult.
The borate most commonly enters the eluent system as a contaminant from degrading deionized water systems, or from borate that leaches from glass eluent bottles.
Glucamine (1-amino-1-deoxy-D-glucitol) resin has been used to remove borate from industrial streams. This chemical reaction involves hydrogen bonding through the oxygen atoms of the borate to the diol groups on the resin. For example, Amberlite.RTM. IRA-743 (Rohm & Haas Co.) has been used for many years to remove borate from water. The Amberlite.RTM. IRA-743 particles are quite large, generally about 1 mm in diameter. This resin is used to bring the borate concentration into the parts per million (ppm) range, which is generally too high for more sophisticated analytical chromatographic methods as peak tailing is not eliminated or sufficiently reduced.
Similarly, a gluconate resin has been used for retaining borate. Sec Cerrai et al., Energia nucleare (Milan) 5: 824 (1958). These authors used a strong base anion exchange resin in the gluconate form to retain borate, as depicted below in structure 1. In this work, the anion-exchange site itself bears the glucanol group, which is exchangeable for other ions under the right conditions, and thus may not be suitable in some applications. ##STR1##
Thus, a need exists for a stable, efficient borate-removing resin for use in chromatography, particularly analytical chromatography.
Accordingly, it is an object of the present invention to provide compositions for use in ion exchange chromatography that can remove borate from the analyte stream prior to detection and thus reduce peak tailing. It is a further object to provide for methods for removing borate from analyte streams.